In override control of an NC apparatus, in general, when a dial (knob) of an override switch provided on a console panel is turned, a feed speed (cutting speed) of a servo axis specified in a machining program is changed at a percentage indicated by a scale of the dial. In general, a fast-forward override and a main axis override can be also set in a similar manner.
According to override control of conventional NC apparatuses, an editing operation of writing an override value in the block in execution can be performed, by inputting an override value from the outside during the execution of the machining program. Thereafter, in executing the same machining program, override is controlled in advance to work at a speed edited by the machining program (for example, see Patent Document 1).
When an override is input during the execution of a machining program, a program number and an override value of the program in execution are stored as a set. At the time of executing the same machining program next time, an override value corresponding to the block number of the program in execution is used from among stored override values, thereby carrying out the operation at the same speed (for example, see Patent Documents 2 and 3).
Patent Document 1: Japanese Patent Application Laid-open No. S63-47805 (Page 1, FIG. 2, FIG. 3)
Patent Document 2: Japanese Patent Application Laid-open No. H05-189020 (Page 1, FIG. 6)
Patent Document 3: Japanese Patent Application Laid-open No. S60-207910 (Page 1)